Minimally invasive posterior cervical facet arthrodesis shim implant and tools therefor

ABSTRACT

The shim-type implant for distraction and fusion of cervical facet joints is provided. The implant has a generally box-like shape with a blunt leading edge that may be centered or offset to the inferior face. The implant may include a graft window for enhanced osseous through-growth after implantation. The implant is coated with hydroxyapatite (HA) and/or tri-calcium phosphate (TCP) to allow for osteo-conduction, is porous, and has a roughened surface with serrations on the superior and inferior faces. The implant may be fabricated from a titanium or tantalum alloy. In an embodiment, a set of tools is provided with a chisel and one or tongs and one or more decorticators for inserting the implant.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application 62/849,850filed May 18, 2019, the contents of which are incorporated by reference.

FIELD OF THE INVENTION

The invention pertains to surgical implants and tools for thedistraction and fusion of cervical facet, foramen, and vertebrae.

BACKGROUND

Cervical spinal surgery since the late 1950s and early 1960s hassteadily transitioned from primarily posterior based to primarilyanterior based. Posterior based surgery has the following majoradvantages: minimal critical structures in the surgical field, familiaranatomy, and access to multiple levels. However, posterior based surgeryhas the following major disadvantages: dissection or approach relatedpost-operative pain and large or limited arthrodesis option (forexample, lateral mass screws and surface area available for fusion).Anterior based cervical surgery addresses some of the deficits,particularly pain and infection rates. Thus, the trend in the UnitedStates has been a shift towards more anterior cervical surgery andtowards less posterior cervical surgery.

However, certain unique risks still remain with anterior surgery: injuryto esophagus, injury to trachea, dysphagia/dysphonia, injury torecurrent laryngeal nerves, carotid artery injury, internal jugular veininjury, vagus nerve injury, adjacent level disease, non-unions, implantfailure, implant prominence, dural injury, spinal cord injury to name afew. Thus, there has been a reemergence of posterior based surgery,particularly minimally invasive posterior surgery, to address the issuesthat may arise with anterior surgery.

Common indications for posterior minimally invasive surgery (MIS)include anterior cervical non-unions, patients at high risk fornon-unions (for example, smokers), and/or isolated foraminal stenosiswhich may lead to radiculopathy. In theory, given that the facet surfacearea of the posterior spine is equal to or larger than the surface areaof the disc space anteriorly in between the uncus, one could minimizethe rate of cervical non-unions or even treat anterior non-unions via aposterior MIS. In theory, if stenosis is present at the foraminal level,indirect decompression via a posterior MIS would elevate the facet jointand increase the foraminal height as has been shown in the literature.In theory, given the minimal disruption of soft tissue with posteriorMIS, the infection rates and post-operative pain issues would match orsurpass that of anterior based surgery.

Two general technologies are currently in use for minimally invasivecervical facet arthrodesis. The first are manufactured allografts, madefrom human bone that is compacted and machined. See for example“FacetLift” implants from Medtronic. These implants have cleardisadvantages. The implants are brittle and can fracture duringinsertion. In addition, these implants are radiographically lucent,which can make intra-operative assessments challenging andpost-operative fusion rates difficult to observe. And, these implantshave small pore sizes (or no pores at all) from the machining processand can result in limited or no bone in-growth and bone fusion.

An alternative cervical facet implant are metal (usually titanium)implants, for example the “CAVUX®” (referred to as “DTRAX®” in someliterature), “HONOUR® ORB,” “Valeo® II C”, “UNIFLEX® Cervical cage” andothers. See, for example, WO 2015/047818 and WO 2009/148619. Theseimplants do not provide for efficient bone in-growth. Rather, theytypically have bone on-growth or through-growth through a limited graftwindow, which is less efficient at bone fusion. In addition, the shapeof prior art implants is not conducive to safe implantation. In someinstances, these implants require harsh insertion techniques, such asmalleting that reduce the control of the implantation procedure. Thecervical facet joints frequently have minor imperfections and bonespurs, and prior art devices can unnecessarily damage these featuresduring implantation.

SUMMARY OF THE INVENTION

The inventive implants provide a novel combination of features thataddress the shortcomings in the prior art discussed above. In variousembodiments, the inventive implants include a titanium or tantalum alloybody that has a similar modulus of elasticity as natural bone andprovides good radiologic contrast. In an embodiment, the inventiveimplants include a rounded nose that limits tissue damage duringinsertion. In an embodiment, the inventive implants include serratedsurfaces on the superior and inferior faces. In an embodiment, the bodyof the inventive implants may be porous, roughened, and coated with anosteoconductive material such as hydroxyapatite (HA) and/or tricalciumphosphate (TCP). In an embodiment, the body of the inventive implantincludes a graft window spanning the entire thickness of the implant.

In an embodiment, implants and methods are provided for treatingstenosis with or without radiculopathy comprising surgical distractionof the relevant cervical vertebrae and insertion of the implant of claim1. In an embodiment, this invention provides a shim implant for thefusion of a cervical facet joint, comprising a generally rounded orbox-shaped body having a distal face, a proximal face, superior andinferior surfaces in a generally parallel orientation, and two sidefaces in a generally parallel orientation, wherein a transverse axis canbe defined as a line perpendicular to the side faces. The distal facemay have a rounded profile defined by an arc having a radius on atransverse axis. The proximal face may have one or more insertion deviceengagement features. The superior and inferior surfaces each compriseserrations with a plurality of grooves on a transverse axis generallyspanning the entire length of a transverse axis. The implant may befabricated from titanium metal or alloy or tantalum metal or alloy, andmay have a roughened surface, and is coated with hydroxyapatite ortri-calcium phosphate or both and is porous to allow for bone in-growth.

In an embodiment, the implant may have a graft window comprising aperforation spanning the distance between the superior and inferiorsurfaces. In an embodiment, the implant may have a rounded profile ofthe distal face is biased towards the inferior surface. In anembodiment, the insertion device engagement features comprise one ormore holes in the proximal face. The insertion device engagementfeatures may comprise three holes aligned on a transverse axis on theproximal face. At least one hole may have female screw threads forengaging a male threaded tool. The threaded hole may be a central holein a group of three holes.

In an embodiment, each surface of the implant may be roughened with amacro surface roughener or nano-coating. In an embodiment, thehydroxyapatite or tri-calcium phosphate coating has a thickness ofapproximately 35 μm. The porous material may have pore sizes ranging in200 to 900 μm.

In an embodiment, a set of tools is provided for implanting the implantdescribed above. The tools include a chisel and one or more tongs andrasps. An entry chisel is provided with a distal end with smoothinferior and superior surfaces, and a uniform cross-sectional profile,wherein the chisel has a shaft with rounded superior and inferiorsurfaces and flattened sides, and wherein the chisel shaft has twocannulation channels running the entire length thereof for accepting aguidewire. In an embodiment, a first tong has two prongs at a distal endthat are smooth or roughened, and a channel in the shaft along theentire length of the tong, and the interior cross-section of the channelmatches the uniform cross-sectional profile of the chisel, such that thechisel can be inserted in the channel in the first tong from a proximalend of the first tong to a nested position. The rounded superior andinferior surfaces and flattened sides of the chisel maintain rotationalstability that prevents the chisel from rotating when in place. Whennested, the distal tip of the chisel may be aligned with the prongs. Thechisel nested in the first tong may be inserted into a channel in aproximal end of a first decorticator, wherein the first decorticator hasa jagged distal end with teeth and the proximal end has a handle formanual manipulation of the decorticator, and wherein the chisel andfirst tong are aligned with the distal edge of the first decorticator,and wherein a facet joint between two vertebrae is decorticated from aposterior approach. The first decorticator may then be withdrawn leavingthe chisel nested in the first tong embedded in the facet joint and thechisel may then be withdrawn. Next, a rasp may then be inserted into thechannel in the first tong. A rasp of various dimensions (width andheight) may be used to remove tissue within the facet joint tofacilitate a fusion and to gauge the width and height of the finalimplant. The rasp is then withdrawn from the channel in the first tong.Next, an inserter having an implant as described above affixed to it isinserted into the channel in the first tong. In an embodiment, theinserter may have a shaft, an axle within the shaft, a handle that turnsthe axle, and a male-threaded connection at the distal end of the axlethat is screwed into the female-threaded engagement feature on theimplant, and at least one prong aligned with another engagement featureon the proximal face of the implant. The inserter is inserted into thechannel in the first tong, and the implant is placed and secured in thefacet joint. The handle is rotated to unscrew the implant and disconnectthe implant from the inserter, and the first tong is withdrawn, leavingthe implant securely in position.

In an embodiment, a second tong may be provided having two prongs at adistal end that are smooth or roughened and a channel in the shaft alongthe entire length of the second tong, wherein the interior cross-sectionof the channel matches the uniform cross-sectional profile of the firsttong. The chisel nested in the first tong is inserted into the proximalend of the channel on the second tong into a nested position wherein thechisel tip, prongs of the first tong, and prongs of the second tong maybe aligned. The chisel nested in the first tong and nested in the secondtong may then be inserted into the facet joint. In an embodiment, thechisel and first tong are withdrawn, and a rasp may be inserted into thechannel in the second tong. Rasps of various dimensions (width andheight) may be manipulated by the surgeon to remove tissue within thefacet joint to facilitate a fusion and to gauge the width and height ofthe final implant. The rasp may then be withdrawn from the channel inthe first tong, and an inserter as described above having an implant asdescribed above affixed to it, is inserted into the channel in thesecond tong, and the implant is placed and secured in the facet joint.The handle may be rotated to disconnect the implant from the inserter,and the second tong is withdrawn, leaving the implant securely inposition.

In an embodiment, a second decorticator may be provided and the chiselnested in the first tong nested in the second tong are inserted thereinto further decorticate the facet joint. In an embodiment, a third tongis provided that the chisel, the first tong and the second tong areinserted within to provide an appropriate space for the implant in afacet joint.

In an embodiment, the width of the space decorticated for the implant inthe facet joint is controlled by the use of one or more tongs, and theheight of the space decorticated for the implant is controlled by theheight of the rasp.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an embodiment of the inventive implantwith a centered nose and without a graft window.

FIG. 1B is a perspective front view of the inventive implant of FIG. 1A.

FIG. 10 is a side elevation view of the inventive implant of FIG. 1A.

FIG. 1D is a front elevation view of the proximal end of the inventiveimplant of FIG. 1A.

FIG. 1E is a back-elevation view of the inventive implant of FIG. 1A.

FIG. 2A is a perspective view from the rear and above of an embodimentof the inventive implant with a centered nose and with a graft window.

FIG. 2B is a perspective front view of the inventive implant of FIG. 2A.

FIG. 2C is a top view of the inventive implant of FIG. 2A.

FIG. 3A is a perspective view from the rear and below of an embodimentof the inventive implant having a nose which is off center and no graftwindow.

FIG. 3B is a front perspective view of the implant of FIG. 3A.

FIG. 4A is a perspective back view of an embodiment of the inventiveimplant with an off-centered nose and a graft window.

FIG. 4B is a front perspective view of the implant of figure of theinventive implant of FIG. 4A.

FIG. 5A, FIG. 5B, and FIG. 5C depict an entry chisel according to anembodiment of this invention.

FIG. 6A, FIG. 6B, FIG. 6C and FIG. 6D depict a first facet tongaccording to an embodiment of this invention.

FIG. 7A, FIG. 7B, FIG. 7C and FIG. 7D depict the entry chisel nestedwithin the first facet tong.

FIG. 8A, FIG. 8B, FIG. 8C and FIG. 8D depict a first decorticator toolaccording to an embodiment of this invention.

FIG. 9A, FIG. 9B and FIG. 9C depict the apparatus as shown in FIG. 7nested inside the first decorticator. The decorticator includes aremovable handle.

FIG. 10A, FIG. 10B, and FIG. 10C depict a second facet tong.

FIG. 11A, FIG. 11B, FIG. 11C and FIG. 11D depict the apparatus of FIG. 7nested inside the second facet tong.

FIG. 12A and FIG. 12B depict a second decorticator according to anembodiment of this invention.

FIG. 13A, FIG. 13B, and FIG. 13C depict the apparatus of FIG. 11 nestedinside the second decorticator.

FIG. 14A, FIG. 14B, and FIG. 14C depict a third facet tong according toan embodiment of this invention.

FIG. 15A, FIG. 15B, FIG. 15C and FIG. 15D depict the apparatus of FIG.11 nested inside the third facet tong according to an embodiment of thisinvention.

FIG. 16A, FIG. 16B and FIG. 16C depict the apparatus of FIG. 15 with theentry chisel removed according to an embodiment of this invention.

FIG. 17A and FIG. 17B depict the apparatus of FIG. 16 with the firsttong removed according to an embodiment of this invention.

FIG. 18A and FIG. 18B depict the apparatus of FIG. 17 with the secondtong removed.

FIG. 19A, FIG. 19B and FIG. 19C depict a rasp tool according to anembodiment of this invention.

FIGS. 20A and 20B show the rasp apparatus inserted into the third tongaccording to an embodiment of this invention.

FIGS. 21A and 21B show an inserter tool according to an embodiment ofthis invention.

FIGS. 22A and 22B depict the inserter tool with an exemplary implantaffixed to the distal end.

FIG. 23 is a cutaway view showing an implant according to an embodimentof this invention affixed to the distal end of the inserter tool.

FIG. 24A, FIG. 24B, and FIG. 24C depict a final set up with a raspnested in the third tong according to an embodiment of this invention.

DETAILED DESCRIPTION

This invention provides an implant for the fusion of cervical spinalvertebrae, tools to insert the implant, and surgical procedures.

Implants

In an embodiment, the implant is a shim 100 with a box-shaped body asshown in FIGS. 1A-1E. For orientation, the shim has a blunt distal endthat would sit anteriorly within the facet joint, also referred toherein as a nose, for insertion in between the cervical facet joints tominimize damage during insertion and reduce the tolerance necessary toinsert the implant without unnecessary damage at the implant insertionsite. The terminology “distal” and “proximal” are in relation to thesurgeon implanting the inventive shim. Thus, the proximal face isclosest to the surgeon during implantation, and the distal face is theleading edge inserted into the body of the patient at the implant site.The distal end of the implant, then, would sit more anteriorly withinthe facet joint, and the proximal end of the implant would sit moreposteriorly within the facet joint.

In an embodiment, the inventive shim 100 has a proximal side with one ormore insertion device engagement features 132 and 134. In an embodiment,the insertion device engagement features are one or more threaded (134)and non-threaded (130) holes or indents adapted to receive appropriatetools used to aid in the implantation of the inventive device. In theembodiment illustrated in the figures, there are three holes in theproximal face of the implant, and the center hole 134 is threaded. In anembodiment, the holes may be drilled into the implant after the body isformed or may be created as the implant is created using additivemanufacturing techniques.

The inventive implants also have a superior face 140 and an inferiorface 142. In an embodiment, the superior and inferior faces both have aseries of parallel grooves or serrations 144 running in a transversedirection.

FIGS. 2, 3, and 4 all illustrate variations on the embodiment of FIG. 1. In FIGS. 2A and 2B, implant 102 is illustrated. This is similar toimplant 100 but also features a graft window 150, that in an embodiment,is an aperture through the entire thickness of the implant 102 from theinferior surface to the superior surface.

FIGS. 3A and 3B show embodiment 104, that is similar to embodiment 100,but with an offset blunt nose 112. FIGS. 4A and 4B show embodiment 106,which has the offset nose and the graft window 150. The blunt nose 112in embodiments 104 and 106 is biased towards the inferior face of theimplant. Put differently, the transverse axis used for the radiusdefining the curvature of the blunt nose is biased towards the inferiorside of the implant. By contrast, the transverse axis used for theradius defining blunt nose 110 in embodiment 100, where blunt nose 110is centered between the inferior and superior sides, is centered betweenthe inferior and superior sides.

Thus, there are at least four embodiments of the shim of this invention:(1) centered blunt nose, no graft window (100); (2) centered blunt nose,with the graft window (102); (3) offset blunt nose, no graft window(104); (4) offset blunt nose, with the graft window (106). Otherembodiments are possible and within the scope of this invention.

The inventive implants are shims that are inserted by distraction of thefacet joints and inserted into position with appropriate tools. In anembodiment, the shims are inserted in between the two facets and withinthe facet joint. In contrast to the prior art devices discussed above,such as the CAVUX®, HONOUR® ORB, Valeo® II C, UNIFLEX® Cervical cages,the inventive implants have a serrated surface, porous structure of thematerial, features which allow osseous in-growth and better fixation ofthe implant and consecutively of the joints. An additional embodiment ofthe instant invention provides a graft window which allows osseousgrowth and may provide additional osseous integration.

In an embodiment, the entire implant is fabricated from medicallycompatible tantalum, titanium, tantalum alloy, or titanium alloy. Forexample, an appropriate titanium alloy may be titanium 6AL4V and 6AL4VELI (ASTM Standard F1472, https://www.astm.org/Standards/F1472.htm (seealso https://en.wikipedia.org/wiki/Ti-6Al-4V)), which are alloys madewith about 6% aluminum and 4% vanadium. An appropriate tantalum alloymay be tantalum alloyed with 2.5% to 10% tungsten, or 40% niobium. Thesematerials are known to have good biocompatibility and match the modulusof elasticity of bone. In an embodiment, the implant may be manufacturedfrom a titanium alloy in accordance with ASTM F136, or where exteriorsurfaces are coated with medical-grade commercially pure titanium (CPTi) per ASTM F1580.

In an embodiment, all surfaces of the implant may be roughened withmacro surface roughness or nano-coating. This may be accomplished with atechnique such as grit blasting, acid etching, or plasma spray coating(also called thermal spray coating).

In an embodiment, all surfaces of the implant are coated withhydroxyapatite (HA) and/or tricalcium phosphate (TCP), with a coatingthickness of approximately 35 μm. HA and TCP are well known asosteoconductive materials that encourage bone growth.

In an embodiment, the implant may be fabricated from a porous materialknown to enhance bone in-growth, for example with pore sizes ranging in200 to 900 μm to facilitate in-growth and have a porosity of 60-65% tomimic cancellous bone. The combination of surface roughness, HA or TCPcoating, and porosity will facilitate in growth which is desirable forfusion.

The inventive shim implants of this invention may be implanted by knownminimally invasive methods. For example, prior to inserting the shimimplant, the patent may be positioned prone with face down and theadequate intra-operative imaging of the desired facet joint(s) isassessed. Then a paracentral stab incision is made in line with andcaudal to the facet joint on the anterior-posterior projection, and ablunt entry dilator or chisel is guided through the soft tissues and isplaced in between the facet joint. A subsequent dilator or series ofdilators is then placed over the initial dilator and into the facetjoint to access the joint space, and the blunt entry chisel or dilatoris removed while the outer most dilator is kept in place. Subsequently,the extra-articular portion of the facet joint is decorticated with adecortication tool used first over and/or around the dilator, and a raspnext within the dilator to decorticate the intra-articular portion ofthe facet joint. Once decortication is complete, the shim implant isinserted under image guidance with a shim inserter device. After theshim implant is in position the shim inserter device is removed. Graftmaterial can optionally be packaged posterior to and around the implantthrough the distractor tool. The dilator tool is then removed, and softtissue closure and dressing are performed. In the detailed descriptionbelow, the subsequent dilators are labeled as tongs.

Tools

In an embodiment, the implants herein may be implanted into a cervicalfacet joint in a posterior approach.

In an embodiment a series of nestable tools are provided to place theimplants of this invention.

In an embodiment, an entry chisel 210 is provided as depicted in FIGS.5A, 5B, and 5C, comprising a shaft having a distal and proximal end. Thedistal end is the tip of the chisel 211, with smooth inferior andsuperior surfaces. The proximal end 212 has a roughened surface. Thedevice may have dual cannulation channels 214. The channels 214 mayaccept a guidewire to guide the placement of the apparatus as discussedherein. The device shaft may have rounded superior and inferior surfaces218 and flat sides 219. The chisel has a uniform cross-sectional profilebecause in the next step, the first tong is inserted using the chisel asa guide (FIG. 7 ). The rounded superior and inferior surfaces and flatsides prevent the first tong from rotating out of plane from the chiselat the next step of the procedure. The chisel further has a series oftransfer perforations (holes) 216 that serve as navigational landmarksfor intra-operative imaging to evaluate the position of the tool duringthe implantation procedure.

Operationally, chisel 210 can be placed with the assistance of guidewires that fit within cannulation channels 214. This feature assists theaccurate placement of the tool during surgery. The chisel position canalso be modified with the use of such guide wires.

FIGS. 6A-6D depict a first tong 230 that entry chisel 210 nestleswithin. The distal end of the first tong 230 has two prongs 234 that maybe smooth or roughened. The proximal end has roughened surface 235 forease of manual manipulation by the surgeon. A central channel 232 runsthe entire length of the tong 230. The profile (i.e., cross section) ofchannel 232 matches the cross section of entry chisel 210. The roundedsuperior and inferior surfaces 218 along the shaft, and flattened sides219 of the chisel shaft ensure rotational stability when the chisel isinserted into channel 232. The tong includes holes 236 forintraoperative imaging of the position of the tool. Because first tong230 may nestle within a second tong (FIG. 11 ), tong 230 has a uniformcross-sectional profile with rounded top and bottom 238 and flattenedsides 239. Tong 230 may also be equipped with attachment point 237providing a firm connection handle 270 (FIG. 9 ).

The embedding of chisel 210 within tong 230 is shown in FIGS. 7A-7D.FIGS. 7A and 7B are two perspective views of the entire tool, viewedfrom the distal end (FIG. 7A) and proximal end (FIG. 7B). Details of thedistal end 242 are shown in FIG. 7C and proximal end 244 are shown inFIG. 7D. In the distal end 242, chisel tip 211 is flush with prongs 234.Proximal end 244 shows the proximal end 212 of entry chisel 210 nestedwithin the channel of tong 230. Proximal end 212 juts beyond theroughened proximal end 235 of tong 230.

The next step in the procedure relies on a first decorticator 250 (FIGS.8A-8D). FIG. 8A is a perspective view from the distal end, and FIG. 8Bis a perspective of the entire tool from the proximal end. FIG. 8C is aclose up of the distal end 255 of decorticator 250 showing additionaldetail. FIG. 8D is a close-up of proximal end 253 of decorticator 250showing additional detail. Decorticator 250 is a round hollow shaft(251) running the length of the tool except for the proximal region 258.Shaft 251 defines channel 252 that runs the length of the tool. Thedistal end 255 has a diagonal cut forming an ellipsis 254 around thedistal end of channel 252. The inferior edge of the distal end ofdecorticator 250 is jagged with teeth 256. The proximal end is depictedwith octagonal cross section 258. Other shapes (besides octagonal) for258 are possible, such as hexagonal or others. The proximal terminus ofchannel 252 is shown in FIG. 8D. Also shown are anchor points 259 forconnection to handle 270 (FIG. 9 ).

As shown in FIGS. 9A-9C, the chisel nested in tong 230 depicted in FIG.7 is inserted into channel 252 of decorticator 250. Handle 270 may beplaced over decorticator 250 to provide a firm grip for the surgeon tomanipulate decorticator or other instruments into position. In theillustrated embodiment, handle 270 includes features such asprotuberance 271 to improve the grip of the surgeon. Also shown iscollar 272 to assist in securing handle 270 to decorticator 250. Thehandle may nest over octagonal section 258 on the decorticator. Theremay also be a mechanism that interacts with holes 259 and 237 to securehandle 270 on decorticator 250.

The decortication procedure involves removal of superficial bone andother tissue to prepare a site for bone grafting for the purpose offusing of the vertebrae or facet joint. When the degree of desiredtissue removal is achieved, the decorticator is removed. If additionaldecortication is needed additional tongs can be layered over the firsttong as discussed in the following paragraphs.

As shown in FIGS. 10A-10C, a second facet tong 280 may be provided,having a distal end with two prongs 284 that may be smooth or roughenedand a proximal end with roughened surface 285. Tong 280 has shaft 281running the entire length of the tool. Within shaft 281 is channel 282,adapted to accept tong 230 within it. Accordingly, the upper and lowersurfaces of channel 282 are rounded and the sides are flat, toaccommodate the cross-sectional profile of tong 230. On tong 280, thesuperior and inferior surfaces 288 are rounded, and sides 289 are flat.Also provided is handle attachment point 287 and a series of transverseperforations 286 for intraoperative imaging of the position of the tool.

FIGS. 11A-11D show the apparatus of FIG. 7 inserted into second tong280. Thus, 294 (FIG. 11C) shows the distal end of this arrangement, withentry chisel 210 nested within first tong 230 and nested within secondtong 280. FIG. 11C shows flattened chisel tip 211 flush with prongs 234(from tong 230) and 284 (from tong 280). The proximal end of thisarrangement is shown in FIG. 11D, which depicts chisel proximal end 212nested within first tong proximal end 236 and nested within second tongproximal end 285.

FIGS. 12A and 12B show a second decorticator 310 that is similar todecorticator 250 only larger to accommodate the apparatus as depicted inFIG. 11 within it. FIG. 12A is a perspective view from the distal end,and FIG. 12B is a perspective of the entire tool from the proximal end.Decorticator 311 comprises a hollow round (in cross-section) shaft 311that runs the entire length of the tool. This shaft is designed to fitentry chisel 210 nested within first tong 230 and nested within secondtong 280 shown in FIG. 11 within it (shown in FIG. 13 ). Distal end 313of decorticator 310 has an inferior edge 316 with jagged teeth fordecorticating bone. Also depicted is a diagonal cut at the distal end tomake ellipsis 314. The proximal end 318 of decorticator 310 is depictedwith an octagonal cross section. Other shapes (besides octagonal) for318 are possible, such as hexagonal or others. The proximal terminus ofchannel 312 is shown in FIG. 12B. Also shown are anchor points 319 forconnection to handle 330 (FIG. 13A).

The apparatus of FIG. 11 is nested within 312 as shown in FIGS. 13A-13C.FIG. 13C is a detail view of distal end of decorticator 310 with entrychisel 210 nested within first tong 230 and nested within second tong280 (294) inserted within channel 312 in the operational position.Handle 330 is than affixed to the proximal end of decorticator 310 asshown. A mechanism is provided to securely affix handle 330 to thedecorticator without allowing the nested chisel and tongs 294 to move.Also shown is collar 332 to assist in securing handle 330 todecorticator 310.

Operationally, the apparatus of FIG. 13 is used to decorticate androughen the bone surfaces on the joint as discussed above (paragraph[0069]). Decorticator 2 is then removed, leaving apparatus 294 in thejoint. If additional distraction or access to a larger surface area isdesired, a third tong 340 may be employed, shown in FIGS. 14A-14C. Tong340 is similar to tongs 280 and 230 but is larger to accommodate theapparatus of FIG. 11 within. Thus, tong 340 has shaft 341 and channel342 running the entire length of the tool. The distal end of tong 340has two prongs 344 that may be smooth or roughened. The proximal end hasa roughened outer surface 345. It can be seen is FIG. 14C showing detailof the proximal end, that channel 342 has an interior cross-sectionmatching the cross-section of the exterior of second prong 280. Alsoshown is anchor point 347 for a handle, and series of transverseperforations 346 for intra-operative imaging to evaluate position of thetool.

FIG. 15 shows the apparatus of FIG. 11 inserted into channel 342. FIG.15A is a perspective view of the entire tool from the distal end. FIG.15B is a perspective view of the entire tool from the proximal end. FIG.15C is a detail view of distal end, showing the entry chisel 210, firsttong 230, second tong 280, and third tong 340 nested together, with eachof prongs 234, 284, and 344 flush with chisel tip 211. The proximal endof this arrangement is shown in FIG. 15D, with each of 212, 235 and 285nested together and within channel 342.

Operational, the apparatus of FIG. 15 is now wedged within the facetjoint at the desired position. At this stage the chisel, first tong, andsecond tong are removed as follows.

First, as depicted in FIGS. 16A-16C, chisel 210 is withdrawn from theapparatus of FIG. 15 . This can be seen clearly in the detail of FIG.16C, showing distal end 353 with channel 232 in facet tong 230 empty.This can also be seen at the proximal end 354 in FIG. 16B, where theproximal end 212 of chisel 210 is absent. Next, first facet tong 230 iswithdrawn to give the apparatus shown in FIGS. 17A and 17B. Finally,second facet tong 280 is withdrawn to give the appearance shown in FIGS.18A and 18B. At this stage prongs 344 are embedded in the facet joint.

Thus, the entry chisel 210 and first, second, and third tongsdecorticate and establish the appropriate width for the implants asdescribed herein. As discussed in the following paragraphs, the heightof the distraction for the implant is established with one or morerasps.

Accordingly, as shown in FIGS. 19A-19C and FIGS. 20-20A, rasp 400 isinserted into facet tong 340. Rasps of various sizes, as discussedherein, are used to further decorticate the facet joint in preparationof placement of implant. Rasp 400 is illustrated with several views inFIGS. 19A-19C. The rasp has a shank 402 running the length from the rasphead at the distal end to the handle at the proximal end. Asillustrated, the shank as a rectangular cross-sectional profile. Therasp head has a roughened superior surface 412 and a roughened inferiorsurface 414, a distal tip 410 and an angled leading edge 416. Theproximal end of rasp 400 is a handle 418 to aid in insertion andremoval.

Rasp 400 is inserted into fact tong 340 as shown in FIGS. 20A and 20B.The head of the rasp (i.e., 416) is flush with fork prongs 344. Shank402 is sized to that handle 418 fits over the proximal end of facet tong340.

The rasp head may be made available in a variety of heights and widths.In terms of width, this rasp can be sized to fit into facet tong 230 or280 or 340. The height of the rasp head is function of the requirementsof the surgery to adjust the facet joint for the desired height of theimplant.

This procedure may only need a smaller size and can rely on a raspinserted into facet tong 230 or 280. Similarly, this procedure may onlyneed a smaller implant that would match the rasp. For illustrativepurposes, the remainder of the procedure is illustrated with facet tong340. Rasps intended for tongs 230 or 280 must have a length appropriateto the tong tool.

The next step is insertion of an implant into facet tong 340. Theimplant is attached to implant inserter 430 (FIGS. 21A and 21B).Inserter 430 has shaft 432 running the length of the tool. Head 433 isat the distal end. In the illustrated embodiment, the distal end hasdual prongs 434 to match the implants (FIGS. 1-4 ) and a centralthreaded head 436 to firmly affix the implant to the tool. The threadedhead has male threads and is rotated by handle 438 on the proximal endof inserter 430. An internal axle 435 (not shown) links handle 438 tothreaded head 436 to screw the implant onto or off the tool. Also shownin FIG. 21A is marker 437 near the proximal end to indicate the implantis flush with facet tongs distally. Only one such marking is shown butmultiple markings may be employed to match various facet tongs.

In an embodiment, the implant affixed to inserter tool 430 is shown inFIGS. 22A, 22B and 23 . Implant 106 is illustrated. To affix the implantto the inserter, male threads 436 are inserted into female threads 134(FIGS. 1-4 ) and screwed into place by rotating knob 438. Prongs 434 arealigned with indents 132 on the implant and male thread 436 are turnedall the way to affix implant 106 to inserter 430. FIG. 23 is a cutawayview of an embodiment of the implant affixed to the inserter tool withmale threads 436 and dual prongs 434.

The implant affixed to the inserter tool is then inserted into facettong 340 as shown in FIGS. 24A-24C. The implant is inserted intoposition and inserter tool 430 is removed by unscrewing the tool fromthe implant by turning knob 438. Additional graft material may be placedthrough facet tong to aid in fusion. The facet tong 340 is removedleaving the implant in position and the surgery is completed.

Thus, the nested series of tongs adjusts the width of the space in thefacet joint for the implant such as 100, 102, 104, or 106, and rasps 400can be produced in various heights to establish the height of the spacefor the implant. For example, if a narrower width is sufficient, thesurgeon may only require the first and second tongs and omit the thirdtong. Similarly, if the anatomical requirements are for an even widerimplant, a fourth or even fifth tong can be employed.

Drawings Legend No. Description 100 Inventive implant, centered bluntnose, no graft window 102 Inventive implant, centered blunt nose, withgraft window 104 Inventive implant, offset blunt nose, no graft window106 Inventive implant, offset blunt nose, with graft window 110 CenteredBlunt nose 112 Offset blunt nose 120 Side face 130 Proximal face 132insertion device engagement indent 134 insertion device engagementindent with threads 140 Superior face 142 Inferior face 144 Serrationsin superior and inferior faces 146 Pores in surface 150 Graft window 200Tool system 210 Entry chisel 211 Flattened smooth Chisel tip, distal end212 Roughened proximal end 214 Cannulations for guidewires (dual) 216Holes in chisel (markers) for intra-operative imaging to evaluateposition of the tool 218 Rounded top and bottom 219 Flattened sides 230Facet tong 1 231 Facet tong 1 shaft 232 Hollow channel in tong 234 Forkprong (dual) 235 Roughened proximal end 236 Holes in shaft forintra-operative imaging to evaluate position of the tool 237 removablehandle attachment point 238 Rounded top and bottom 239 Flattened sides240 Entry chisel nested inside facet tong 1 242 Distal end of Entrychisel nested inside facet tong 1 244 Proximal end of Entry chiselnested inside facet tong 1 250 Decorticator 1 251 Decorticator hollowshaft 252 Central hollow channel, cannulation to fit over tong 1 253Decorticator proximal end 254 distal end elliptical shape 255Decorticator distal end 256 Distal end with jagged teeth 258 Proximalend with octagonal cross section 259 Holes in proximal end for anchoringwith tool 270 270 Handle 271 Grip protuberance 272 Handle collar 274Chisel and tong 1 nested inside decorticator 280 Facet tong 2 281 Facettong 2 shaft 282 Channel to fit over facet tong 1 284 Fork prong in tong2 (dual) 285 Roughened proximal end 286 Holes in shaft 287 removablehandle attachment point 288 Rounded superior and inferior surfaces 289Flat sides 294 Chisel nested in tong 1 nested in tong 2 distal end 296Chisel nested in tong 1 nested in tong 2 proximal end 310 Decorticator 2311 Decorticator 2 shaft 312 Central hollow channel, cannulation to fitover tong 2 313 Distal end of decorticator 2 314 distal end ellipticalshape Decorticator 2 316 Distal end with jagged teeth Decorticator 2 318Proximal end with octagonal cross section Decorticator 2 319 Holes inproximal end for anchoring with tool 270 Decorticator 2 330 Handle fordecorticator 2 332 Collar for Handle for decorticator 2 334 Chisel, tong1, decorticator 1, tong 2 nested in decorticator 2 340 Facet tong 3 341Facet tong 3 shaft 342 Channel to fit over facet tong 2 344 Fork prongin tong 3 (dual) 345 Roughened distal end tong 3 346 Holes in tong 3shaft 347 Holes in distal end 348 Flat internal sides of tong 3 channel349 Rounded top and bottom interior surfaces of tong 3 channel 351Chisel, tong 1, tong 2 tong 3 nested together distal tip 353 Distal tipof 351 but with chisel removed, tong 1, tong 2 tong 3 nested together354 Proximal end of tong 1, tong 2, tong 3 nested together 355 Distaltip of 351 with chisel and tong 1 removed, tong 2, tong 3 nestedtogether 356 Proximal end of tong 2, tong 3 nested together 400 rasp 402Rasp shank 410 Rasp distal end 412 Rasp roughened superior end surface414 Rasp roughened inferior end surface 416 Rasp angled leading edge 418Rasp handle 420 Rasp nested in tong 3 430 Implant inserter 432 Implantinserter shaft 433 Implant inserter distal end 434 Outer Implant prong(dual) 435 Implant inner shaft (not shown) 436 Central implant prongthreaded 437 Markings on shaft proximally to indicate the implant isflush with facet tongs distally (only one such marking is drawn butmultiple markings would be employed to match various facet tongs) 438Handle to unscrew central prong 439 Roughened distal end 440 Implantinserter nested in tong 3 442 Distal end of Implant inserter nested intong 3 444 Proximal end of Implant inserter nested in tong 3

The invention claimed is:
 1. A set of tools for implanting a shimimplant for the fusion of a cervical facet joint from a posteriorapproach, the implant comprising a generally rounded or box-shaped bodyhaving a distal face, a proximal face, superior and inferior surfaces ina generally parallel orientation, and two side faces in a generallyparallel orientation, wherein a transverse axis can be defined as a lineperpendicular to the side faces, a. wherein the distal face has arounded profile defined by an arc having a radius on a transverse axis,wherein the proximal face has one or more insertion device engagementfeatures; b. wherein the superior and inferior surfaces each compriseserrations with a plurality of grooves on a transverse axis generallyspanning the entire length of a transverse axis; and c. wherein theimplant is fabricated from titanium metal or alloy or tantalum metal oralloy, and has a roughened surface, and is coated with hydroxyapatite ortri-calcium phosphate or both and is porous to allow for bone in-growth;d. wherein the tools comprise an entry chisel with a distal end withsmooth inferior and superior surfaces, and a uniform cross-sectionalprofile, wherein the chisel has a shaft with rounded superior andinferior surfaces and flattened sides, and wherein the chisel shaft hastwo cannulation channels running the entire length thereof, wherein eachchannel is adopted for accepting a guidewire; e. wherein a first tonghas two prongs at a distal end that are smooth or roughened, and achannel in the shaft along the entire length of the first tong, and theinterior cross-section of the channel matches the uniformcross-sectional profile of the chisel, such that the chisel can beinserted in the channel in the first tong from a proximal end of thefirst tong to a nested position, and wherein the rounded superior andinferior surfaces and flattened sides of the chisel maintain rotationalstability and the distal tip of the chisel is aligned with the prongs;f. wherein the chisel nested in the first tong is inserted into achannel in a proximal end of a first decorticator for decorticating afacet joint between two vertebrae from a posterior approach, wherein thefirst decorticator has a jagged distal end with teeth and the proximalend has a handle for manual manipulation of the decorticator, andwherein the chisel and first tong are aligned with the distal edge ofthe first decorticator; g. wherein following the decorticating step, thefirst decorticator is withdrawn leaving the chisel nested in the firsttong embedded in the facet joint and the chisel is then withdrawn, and arasp is inserted into the channel in the first tong, wherein the rasp ismanipulated by the surgeon to remove tissue to facilitate a fusion andto gauge the height of the final implant, and wherein the rasp iswithdrawn from the channel in the first tong; and h. wherein a shimimplant is placed and secured in the facet joint with an inserter havinga shim implant affixed thereto with a shaft, an axle within the shaft, ahandle that turns the axle, and a male-threaded connection at the distalend of the axle that is screwed into the female-threaded engagementfeature on the implant, and at least one prong aligned with anotherengagement feature on the proximal face of the implant, wherein theinserter is inserted into the channel in the first tong, for placementof the shim implant; and wherein the handle is turned to disconnect theimplant from the inserter, and the first tong is withdrawn, leaving theimplant securely in position.
 2. The set of tools according to claim 1,wherein a second tong is provided having two prongs at a distal end thatare smooth or roughened and a channel in the shaft along the entirelength of the second tong, wherein the interior cross-section of thechannel matches the uniform cross-sectional profile of the first tong,wherein the chisel nested in the first tong is inserted into theproximal end of the channel on the second tong into a nested positionwherein the chisel tip, prongs of the first tong, and prongs of thesecond tong are aligned; wherein the chisel nested in the first tongnested in the second tong are inserted into the facet joint and thechisel and first tong are withdrawn, and a rasp is inserted into thechannel in the second tong, wherein the rasp is manipulated by thesurgeon to remove tissue to facilitate a fusion and to gauge the heightof the final implant, and wherein the rasp is withdrawn from the channelin the first tong, and an inserter according to claim 1 having a shimimplant affixed thereto, wherein the inserter is inserted into thechannel in the second tong, and the implant is placed and secured in thefacet joint; wherein the handle is turned to disconnect the implant fromthe inserter, and the second tong is withdrawn, leaving the implantsecurely in position.
 3. The set of tools according to claim 2 wherein asecond decorticator is provided and the chisel nested in the first tongnested in the second tong are inserted therein to further decorticatethe facet joint.
 4. The set of tools according to claim 1, wherein athird tong is provided that the chisel, the first tong and the secondtong are inserted within to provide an appropriate space for the implantin a facet joint.
 5. The set of tools according to claim 1, whereinrasps of varying height and width are used to facilitate a fusion and togauge the height of the final implant.
 6. The set of tools according toclaim 1, wherein the width of the space decorticated for the implant inthe facet joint is controlled by the use of one or more tongs, and theheight of the space decorticated for the implant is controlled by theheight of the rasp.